Applicant's disclosure is directed to a wireless communications network overlay for determining the location of mobile appliances.
The use of wireless communication devices such as telephones, pagers, personal digital assistants, laptop computers, etc., hereinafter referred to collectively as “mobile appliances”, has become prevalent in today's society. Recently, at the urging of public safety groups, there has been increased interest in technology which can determine the geographic position, or “geo-locate” a mobile appliance in certain circumstances. For example, the Federal Communication Commission (FCC) has issued a geo-location mandate for providers of wireless telephone communication services that puts in place a schedule and an accuracy standard under which the providers of wireless communications must implement geo-location technology for wireless telephones when used to make a 911 emergency telephone call (FCC 94-102 E911).
In addition to E911 emergency related issues, wireless telecommunications providers are developing location-enabled services for their subscribers including roadside assistance, turn-by-turn driving directions, concierge services, location-specific billing rates and location-specific advertising.
To support FCC E911 rules to locate wireless 911 callers, as well as the location enabled services, the providers of wireless communication services are installing mobile appliance location capabilities into their networks. In operation, these network overlay location systems take measurements on RF transmissions from mobile appliances at base station locations surrounding the mobile appliance, and estimate the location of the mobile appliance with respect to the base stations. Because the geographic location of the base stations is known, the determination of the location of the mobile appliance with respect to the base station permits the geographic location of the mobile appliance to be determined. The RF measurements of the transmitted signal at the base stations can include the time of arrival, the angle of arrival, the signal power, or the unique/repeatable radio propagation path (radio fingerprinting) derivable features. In addition, the geo-location systems can also use collateral information, e.g., information other than that derived for the RF measurement to assist in the geo-location of the mobile appliance, i.e., location of roads, dead-reckoning, topography, map matching etc.
In a network-based geo-location system, the mobile appliance to be located is typically identified and radio channel assignments determined by (a) monitoring the control information transmitted on radio channel or wire line interface for telephone calls being placed by the mobile appliance to detect calls of interest, i.e., 911, (b) a location request provided by a non-mobile appliance source, i.e., an enhanced services provider. Once a mobile appliance to be located has been identified and radio channel assignments determined, the location determining system is first tasked to determine the geo-location of the mobile appliance, and then directed to report the requesting entity or enhanced services provider.
The monitoring of the RF transmissions from the mobile appliance or wire line interface to identify calls of interest is known as “tipping”, and generally involves recognizing a call of interest being made from a mobile appliance and collecting the call setup information. Once the mobile appliance is identified and the call setup information is collected, the location determining system can be tasked to geo-locate the mobile appliance.
FIG. 1 shows a conventional mobile-appliance communication system having a mobile switch controller 45 connected to base stations 10 for communicating with a mobile appliance 20. Each base station 10 contains signal processing equipment and an antenna for transmitting to and receiving signals from the mobile appliance as well as other base stations and centrally located control and processing stations. A mobile appliance location determining sensor 30 may be positioned at some or all of the base stations 10 to determine the location a mobile-appliance within the signal coverage area of the communication system. The antenna may be a multi-element antenna.
A network overlay system is generally composes of two main components, one that resides at the base station that makes measurements on the RF signal emanating from the wireless device, the wireless location sensor 30 and one that resides at the mobile switch that tasks the wireless location sensor groups to collect data and then uses the data to compute a location estimate, this component generally referred to as the Geolocation Control System (GCS) 50. In the normal course of operation, the GCS is tasked by an outside entity to generate a location estimate on a particular mobile appliance. The tasking is accompanied by information on the mobile of interest including the serving base station and sector for the call and the RF channel (frequency, time slot, CDMA code, etc.) being used by the wireless communications network to complete the wireless connection. Once the GCS receives this tasking, based on the serving sector, it tasks a set of WLS units to make measurement on the RF emission of the mobile. The WLS units make the measurements, and report them to the GCS. The GCS then computes a location estimate using some mathematical or data matching algorithm. Alternatively, RF or wired links containing control channels used to set up calls in the wireless network can be scanned to detect the placement of a call of interest. The signaling that occurs on an RF control channel can be used to determine location, or RF traffic channel parameters can be extracted from the control channel messaging to determine which traffic channel to use for location related measurements
The signal reception area of a base station is generally divided into sectors of various orientations depending on the type of antenna configuration and signal processing equipment. FIG. 2 shows a typical base station coverage area divided by sectors each with a 120 degree bandwidth. The mobile appliance communication system is designed so that the mobile appliance preferably has the capability to communicate with at least one base station while in the coverage area.
The capability of the base stations to receive signals from the mobile appliance is base on a number of factors such as geographic location of the base station with respect to the location of the mobile appliance, the height of the antenna, the number of sectors and the orientation of the sectors.
To meet the ever growing demand for mobile communication, wireless operators are using smart antennas to unlock fixed cell site sectorization to manage and distribute traffic loading more effectively. The geographic distribution of traffic across a network even within a single cell varies considerably, in a typical three sector cell as shown in FIG. 2, the traffic density in the most heavily loaded sector 201 is often more than twice that in the least-loaded sector 203.
As a result, some cells may have sectors that are fully loaded and where traffic is blocking up, while other sectors of the same cell are well below peak loading and have spare capacity, On a larger scale, high traffic areas such as highway interchanges, urban centers and shopping centers create hot spots that strain capacity even while other network resources go unused in low-traffic areas. This variability in the traffic density creates network inefficiencies which have economic effects on the wireless operators.
The use of smart antennas allow wireless operations to control and optimize coverage with flexibility and precision. Again, working within a three 3 sector configuration, operators can adjust sector orientation by pointing angles in 30 degree increments, select from beam widths of 60, 90, 120, 180 and 240 degrees, and change gain settings to expand or contract coverage in highly localized areas, without the expense of a custom antenna.
Using this flexible configuration options of smart antenna, operators can tailor a cell's coverage to fit its unique traffic distribution, thus operators can significantly benefit from matching usage levels with an appropriate sector beam width. A relatively narrow beam width 30 degrees to 60 degrees horizontal, for instance might cover a heavy handoff area or a highway corridor, while a moderate beam width 90 degrees horizontal might serve a suburban or light urban area. In low traffic areas such as mountains, water or rural environments antennas with wider bandwidths can provide the most effective use of network resources.
Operators also can use smart antennas to respond quickly to time varying traffic patterns. Using the system's operation and administration software, operators can adjust sector configurations on demand and within minutes. As a result, operators can modify a cell's operation based on the time of day or day of the week, or to accommodate and anticipated surge in call volume from a sporting or community event.
Operators using smart antennas to change the size or orientation of sectors can shift the traffic load from an overtaxed sector to one or more underused sectors, thus in effect, routing network capacity where and when it is required. For example, a comparison can be made between FIG. 2 where conventional sectors are illustrated and FIGS. 3a and 3b illustrating the controllable sectors enabled with the use of a smart antenna. In FIG. 2 traffic loads across the three sectors 200 vary greatly, with a single sector 201 handling traffic for the office park 211 and most of the residential area 212. By contrast, the cell's sectors 300 in FIGS. 3a and 3b have been resized and reoriented to the traffic load is more evenly distributed among the three sectors. Each sector's beam width has been altered to best accommodate the peak traffic load in that sector. In FIG. 3a the narrow sector 301 covering the office park 211 maximizes capacity for a high traffic area, while the relatively wide sector 303 covering the water 214 provides adequate capacity for a low-traffic area. And as shown FIG. 3b, the sectors can be redefined to provide narrow sector 303 coverage to the football stadium 215 when a large event is taking place.
Smart antennas refer to antennas that spatially steer or switch beams or nulls, or dynamically reallocate available RF channels to different sectors in a base station. In general, they do this as a function of the loading on the base station, or based on the direction of arrival of the RF energy from mobile appliances. The purpose of these functions as discussed above is to extend base station range, improve signal quality, and/or increase the number of users served by the base station. Smart antennas are generally made up of antenna arrays, and accompanying electronics boxes. FIG. 4 shows the principal system elements of a smart antenna. The smart antenna 400 typically consists of a sensor array 401 (antenna array), a pattern-forming network 410 and the adaptive processor 413. The pattern-forming network 410 and the adaptive processor 413 make up the electronic box referred to earlier. The antenna array 401 consists of N antennas 402 designed to receive (and transmit) signals. The physical arrangement of the array (linear, circular, etc.) is arbitrary, however, the physical arrangement fundamentally dictates the capability of the smart antenna 400. The output of each of the N antenna element 402 is fed into the pattern-forming network 410, where the outputs are processed by filters 411. These filters determine the directional pattern of the smart antenna. The outputs of the filters 411 are then summed 412 to form the overall output y(t). The complex weights of the filters 411 are determined by the adaptive processor 413.
Smart antennas can operate on either the forward link, reverse link, or both. Smart antennas can be a part of the base station hardware supplied by the infrastructure vendor, or an appliqué supplied by a third part vendor. In general, the operation of the smart antenna (null/beam steering/switching or channel sector switching) is not known to the rest of the host base station or the wireless infrastructure.
Network overlay location systems typically locate a mobile appliance on the traffic channels of a wireless network. The system typically uses sensors employing techniques of time difference of arrival (TDOA) supplemented with Angle of Arrival (AOA) in some cases to perform a multi-site location computation. The traffic channel assignment information is provided through a separate process, with one option being a wire line interface between the MPC 40 and the GCS 50 (FIG. 1) providing MOBINFO (IS-41 Mobile information) parameters passed by the Mobile Positioning Center (MPC) 40 (FIG. 1) as part of the GPOSREQ (J-STD-036 Geolocation Position Request) message. Another option for the traffic channel assignment data is the wire line interface 41 between the base stations and the mobile switch center (MSC) 45. Neither the base station 10 nor the switch knows that a smart antenna is serving a call. Therefore the GPOSREQ information from the MPC is not able to alert the Geolocation system that a smart antenna is in use. Geolocation systems locate the transmitter using the corresponding MOBINFO parameters passed from the MPC 40. In the case of a mobile served by a smart antenna, information provided to the location system by the MPC on the serving sector may or may not be accurate. The smart antenna may have moved the RF channel from the original serving sector to another to accommodate current traffic needs, or could have spatially steered a beam or null that moves the original coverage of area of a sector to a new geographic area. The overall affect of these smart antenna functions is that the mobile of interest may or may not be in the original geographic area defined by the sector communicated to the location system by the MPC 40 which can frustrate the geo-location process.
For example, FIG. 5a shows a communication system with 7 base stations and their associated overage areas 501. A base station 510 is designated to operate in a three-sector mode (A 511, B 512, and C 513). The infrastructure equipment (mobile switch, not shown) contains data that indicates what RF channels are mapped to what sectors at the base station 510. In the example shown channels u and v, w and x and y and z are mapped (assigned) to sectors A 511, B 512 and C 513 respectively. Without a smart antenna operating, when a mobile 500 is provided service on a traffic channel, the sector serving the mobile would be known by the mobile switch (sector A 511) based on the assigned RF channel/traffic channel (channel v). The geo-location system would task sensors in the vicinity of the serving A sector area, namely sensors in sector 523 of base station 520, and sector 533 of base station 530 to locate the mobile. Other sectors can also be tasked on their vicinity to the serving sector, however only the two closest are shown for clarity of illustration.
If a smart antenna is operating at base station 510, then the smart antenna can move the assigned RF channel, z from sector C 513 to another sector A 511 through an RF switch in the smart antenna to accommodate extra traffic seen on the A sector 511 for this time of day (perhaps a major commuter route is served by the A sector 511, and additional RF channels are allocated to serve it by taking channels from the C sector 513). Prior art geo-location systems attempt to locate the mobile by tasking sensors around the C sector 513, since z is mapped to C, and the smart antenna and its dynamic allocation of channels and variations in sectors is invisible to the base station and the MPC. The sensors in sector 542 of base station 540 and sector 551 of base station 550 as shown in FIG. 5b would be tasked to locate the mobile 500. Thus a poor or perhaps no location would be estimated because the sensors tasked are not the one in proximity to the actual location of the mobile appliance.
Similarly as shown in FIG. 5c, if the smart antenna changed the beam width and orientation of the of the sectors by narrowing the A sector to cover a particularly dense traffic area and widened the beam width of B sector 512, prior art geo-location systems attempting to locate mobile appliance 500 would assume the mobile is in the pre-assigned coverage area occupied by sector A 511. Therefore the system would tasks sensors in sector 561 in base station 560 and sector 573 in base station 570 to locate the mobile. However, as before these are not the sectors closest in vicinity to the mobile and thus a poor location would be estimated.
Additionally, the RF signals from the mobile must pass through the smart antenna array and the accompanying electronics. These entities add delay to the time of arrival of the RF when compared to the normal path delay that would be encountered at the base station without a smart antenna present and thus can lead to inaccurate location results when time-based location techniques such as TDOA are used.
Therefore with the increased used of smart antennas for dynamically adjusting the coverage sectors, there is a need for a geo-location system which is capable of use with communication system which implement sector modifications with smart antenna.
In view of this need, it is the object of the present disclosure to obviate the deficiencies in the prior art and present a method for determining a location of a target mobile appliance, in a wireless communication system with a network overlay geo-location system. The wireless system includes plural base stations and a MPC, each of the base stations include pre-assigned sectors defining a coverage area. One of the base stations includes a smart antenna. The method includes the steps of determining the serving sector from the pre-assigned sectors and using a database to determine if the serving sector's base station has a smart antenna. The method involves scanning antennas elements of the serving sector's base station, prior to pattern forming, for the target mobile appliance's signal to find the actual sector for the mobile appliance. The system then tasks sensors in proximity of the actual sector to locate the mobile appliance.
It is also an object of the present disclosure to present a novel method for determining the location of a target wireless appliance in a network overlay geo-location system for wireless appliances operating in a host wireless communication system. The host system includes a several base stations including sectors defining a coverage area, and one of the base stations employs a smart antenna. The host system also includes a mobile positioning center which provides the geo-location system with information parameters to assist in the location acquisition of the wireless appliance. The method determines a sector of interest from the information parameters and tasks sensors near each sector of the sector of interest base station to locate the mobile appliance.
It is another object of the present disclosure to present a novel method for determining the location of a mobile appliance independently of sector information provided by the MPC. The wireless communication system having a network overlay geo-location system including plural base stations and an MPC. The base stations having assigned channels for each sector representing a coverage area, and one or more of the base stations include smart antennas for adapting the sectors within the coverage area including reassignment of channels. The method entails tasking plural geo-location sensors in the geo-location system to search for the signal and selecting a set of sensors based on the mobile appliance's signal parameters at each sensor and locating the mobile appliance with the set of sensors.
It is still another object of the present disclosure to present a novel improvement for a method of locating a mobile appliance operating in a wireless communication system with at least one base station employing a smart antenna. The method including receiving mobile information from a MPC, including information for determining an assigned sector, and tasking geo-location sensors proximate to a search area to locate the mobile appliance. The improvement includes for each antenna output associated with the assigned sector's base station, measuring a parameter of the mobile appliance's signal; and, selecting the search area based on the measured parameters.
It is yet another object of the present disclosure to present a novel method for determining the location of a target wireless appliance from the target wireless appliance's signal parameters measured at plural geo-location sensors. The method including determining from a database which geo-location sensors are located at base stations with smart antennas; adjusting the measured parameters from geo-location sensors located at base stations with smart antenna; and, determining the location of the mobile appliance from the adjusted measured parameter.
It is an additional object of the present disclosure to present a novel wireless communication system with a network overlay geo-location system having a plurality of sensors located at plural base stations. The system includes a base station with a smart antenna, the smart antenna having an antenna array and a pattern-forming network. The system also has a mobile positioning center in communicational connection with the network overlay geo-location system. The sensors of the network overlay geo-location system being connected to the smart antenna at an interface between the antenna array and the pattern-forming network.
It is yet an additional object of the present disclosure to present an improved network overlay geo-location system in a wireless communication system with a host base station having a smart antenna. The smart antenna including an antenna array and a pattern-forming network and the sensors are connected to the smart antenna at an interface between the antenna array and the pattern forming network.
It is still an additional object of the present disclosure to present a novel method for locating the mobile appliance. The method includes the steps of: retrieving serving sector information from the mobile position center, determining from a database if the serving sector is at a base station with a smart antenna and switching a network overlay geo-location system to a selected one of two different operating modes based on the determination.
These objects and other advantages of the disclosed subject matter will be readily apparent to one skilled in the art to which the disclosure pertains from a perusal or the claims, the appended drawings, and the following detailed description of the preferred embodiments.